1. Field of the Invention
The present invention relates to a driving method of an active matrix liquid crystal display panel, and particularly to a method for driving an active matrix liquid crystal display panel that can provide displaying of clear images.
2. General Background
Liquid crystal display (LCD) panels that are lightweight, thin and portable are widely used in consumer products such as LCD-TVs, notebooks, desktop computers, mobile phones and personal digital assistants (PDAs). The application of LCD panels in the market is becoming more and more important. However, liquid crystal molecules used in LCD panels are sticky. This means that the response time of the liquid crystal molecules of an LCD panel is far inferior to that of an electron gun in a conventional cathode ray tube (CRT) display. In addition to switching the active switching elements, the response time of an LCD panel must generally be shorter than 16.7 ms (milliseconds). Otherwise, the quality of a motion picture displayed by the LCD panel and viewed by the human eye may be very poor.
FIG. 3 schematically illustrates certain parts of a conventional active matrix liquid crystal display panel 100. The active matrix liquid crystal display panel 100 includes n rows of parallel scan lines 101, and m columns of parallel data lines 102 orthogonal to the n rows of parallel scan lines 101. The active matrix liquid crystal display panel 100 also includes a plurality of thin-film transistors (TFTs) 104, which function as switching elements to drive corresponding pixel electrodes 103. Each of the TFTs 104 is positioned near where a corresponding scan line 101 and corresponding data line 102 cross. A gate electrode 1040 of the TFT 104 is electrically coupled to the scan line 101, and a source electrode 1041 of the TFT 104 is electrically coupled to the data line 102. Further, a drain electrode 1042 of the TFT 104 is electrically coupled to the pixel electrode 103. Each scan line 101 includes m pixel electrodes 103, and each pixel electrode 103 and a respective common electrode 105 cooperatively form a capacitor 107.
Reference is made to FIGS. 4A, 4B, and 4C. FIG. 4A illustrates a waveform diagram of voltage supplied to the gate electrode 1040 of one TFT 104. FIG. 4B illustrates a waveform diagram of voltage supplied to the source electrode 1041 of the TFT 104. FIG. 4C illustrates a waveform diagram of voltage of the pixel electrode 103 of the TFT 104.
During the first frame, e.g. a period between t1 and t3, a gate electrode driving device (not shown) supplies a scanning voltage Vg to drive the gate electrode 1040 of the TFT 104. After the TFT 104 is turned on, a source electrode driving device (not shown) supplies a gray scale voltage Vd to the pixel electrode 103 through the source electrode 1041 and the drain electrode 1042 of the TFT 104. Thereby, the pixel electrode 103 is charged to a voltage Vp1 while the gray scale voltage Vd is maintained. When t is equal to t2, the TFT 104 is turned off by turning off the supply of the scanning voltage Vg, whereupon the capacitor 107 maintains the voltage Vp1 until the TFT 104 is turned on at t=t3.
Similarly, during the second frame, when t is equal to t3, the scanning voltage Vg is supplied to drive the TFT 104. The pixel electrode 103 is charged to a voltage Vp2 while the gray scale voltage Vd is maintained. At t=t4, the TFT 104 is turned off by turning off the supply of the scanning voltage Vg, whereupon the capacitor 107 maintains the voltage Vp2.
Because liquid crystal molecules used in the active matrix liquid crystal display panel 100 are sticky, the pixel electrode 103 cannot be charged to the required gray voltage within one frame period of 16.7 ms, and the liquid crystal molecules do not complete their transition to the new alignment in time. As a result, an afterimage of this current frame is perceived on the retina of a viewer's eye, so that the viewer's perception of the image of the next frame will be affected by the afterimage of the current frame. Thus the active matrix liquid crystal display panel 100 fails to provide clear images.
U.S. Pat. No. 5,495,265 entitled “Fast response electro-optic display device” discloses a conventional overdrive method to overcome blurred images. The method relates to an inter-gray response and a look-up table. Data of the look-up table is an overdrive voltage applied to the pixel electrode in order to reduce the response time of the liquid crystal molecules. The overdrive gray-scale voltage is dependent on the previous frame gray scale and subsequent frame gray scale, so that it takes less than 16.7 ms to change the brightness of the pixels between different gray scales. When the levels of gray scales are increased, the data is interpolated by the gray-scale voltages between the previous frame and the subsequent frame of the look-up table. The number of data is increased in geometric series. For example, if the level of gray scale is 8 digits, the size of the look-up table used to store these data should have 8×8=64 digits. That is, the higher the number of gray scales, the larger the size of the look-up table. If the size of the look-up table is increased, the cost of the device is also higher. In some cases, a smaller-sized look-up table can be used, or associated hardware can be implemented to replace the look-up table. However, with these alternative configurations, the performance of the device is not optimal.
Therefore, there is a need for a method for driving an active matrix liquid crystal display panel that can display clear images efficiently.